Aromatic amino compounds as represented by an arylamine and, particularly, a triarylamine and a diarylamine are useful as starting materials of medical and agricultural chemicals, as organic functional materials and as intermediate products therefor. In recent years, they have been used as organic EL materials and organic electrically conducting materials or intermediate products therefor, and are finding ever increasing importance.
As a method of synthesizing the triarylamine and the diarylamine, there has been known, for example, a method that reacts an aryl halide with a monoarylamine by using a copper catalyst. The above reaction has been called Ullmann reaction (see, for example, a non-patent document 1).
However, the Ullmann reaction requires a high reaction temperature and is accompanied by such defects that the obtained aromatic amino compounds (e.g., triarylamine and diarylamine) are colored conspicuously and that the yields are, usually, low due to the formation of by-products in large amounts. Besides, the obtained aromatic amino compounds must be refined requiring much work causing a defect of an increased cost of production.
In order to improve such defects, attempts have been made to lower the reaction temperature by adding a compound that can be coordinated in copper which is a reaction catalyst so that the object product can be obtained maintaining a high purity. For example, there have been reported methods capable of obtaining in high yields the object aromatic amino compounds through the reaction at such relatively low temperatures as 110 to 135° C. by adding a phenanthroline, a bipyridyl or a diamine compound such as cyclohexanediamine (see, for example, non-patent documents 2 to 4).
There has, further, been reported an example of conducting a reaction by adding a 1,1′-binaphthyl-2,2′-diol (see, for example, a non-patent document 5).
According to these examples, the reaction can be conducted under mild conditions and, besides, the object product can be obtained in good yields. However, the compound to be added is so expensive that there remains a problem from the standpoint of cost of production hindering the way toward putting the methods into practice.
There has, further, been known a method of conducting the reaction by increasing the basicity of the reaction system by adding a crown ether (see, for example, a patent document 1). However, the crown ether, too, is an expensive compound which makes the production method never advantageous from the standpoint of cost, and does not make the production method practicable.
There has, further, been known the Ullmann reaction for forming an alkylarylamine by reacting an alkylamine with an aryl halide in the presence of a copper catalyst, and there has been reported an example of the Ullmann reaction using an aromatic oxycarboxylic acid (concretely, a 2-hydroxybenzenecarboxylic acid) having a hydroxyl group and a hydroxycarbonyl group bonded to the neighboring carbon atoms thereof (see non-patent document 5). According to this example, however, the object product was not at all obtained, and no effect was recognized despite of using the aromatic oxycarboxylic acid.
There has, further, been proposed a method of producing an arylamine relying on the Buchwald-Hartwig reaction by using, as a catalyst, palladium-phosphine complex that has a trialkylphosphine as a ligand (see, for example, a patent document 2). According to this production method, however, the reaction must be conducted in a strictly controlled inert gas atmosphere to maintain activity of the palladium-phosphine complex. Besides, the trialkylphosphine itself which serves as a ligand is very unstable in the air, and must be stored and weighed in the inert gas atmosphere hindering the attempt for putting the method into practice. Besides, palladium is very expensive and the phosphine compound used as the ligand is expensive, too, making it difficult to place the method in practice.